Currently, an optical communication device may be packaged in the interior of a so-called electronic instrument. Such an optical communication device includes, for example, an optical transmitter, M optical waveguides, and an optical receiver. The optical transmitter converts M electric signals, which are externally input, into M optical modulation signals and emits the optical modulation signals as light beams in parallel.
The M optical waveguides allow the M optical modulation signals emitted as the light beams in parallel to be transmitted in parallel. The optical receiver receives the M optical modulation signals, transmitted in parallel, through the M optical waveguides, to convert the M optical modulation signals into M electric signals.
An optical transmitter in such an optical communication device as described above simply includes M light-emitting elements, such as semiconductor lasers, and M optical modulators. In such an optical transmitter, M optical modulators individually modulate light beams individually emitted from M light-emitting elements.
However, current semiconductor lasers has insufficient reliability compared to usual electronic circuits and may become unusable at unexpected timing. In such a configuration as mentioned above, an overall optical transmitter becomes unusable even if one of M semiconductor lasers becomes unusable.
In order to solve the above, there has been proposed an optical transmitter in which one semiconductor laser is used, a light beam from the laser is optically distributed into M light beams in parallel through optical fibers and the like, and the M light beams are individually modulated by M optical modulators, to make optical modulation signals (for example, see Patent Literature 1).